Oxygen-related thermal donors generated generally form less effectively in multicrystalline than in Czochralski grown monocrystalline silicon. In addition to a lower interstitial oxygen concentration, carbon and extended crystallographic defects are possible candidates that can account for this feature. To isolate the potential effect of extended defects, we investigate the formation of thermal donors in a carbon-lean Czochralski-grown multicrystalline ingot, resulting from a structure loss during growth. The grain orientations and the densities of dislocations are characterized and are shown to be representative of typical multicrystalline silicon. Eventually, we demonstrate that the macroscopic thermal donor formation kinetics are not affected either by grain boundaries or by dislocations, in contrast with previous findings from the literature. Our results indirectly support the role of carbon as the main thermal donor inhibitor in multicrystalline silicon.